Peter Lighthall, P.Eng. Consulting Geotechnical Engineer

3755 North Naramata Road Naramata, B.C. Canada V0H 1N0 (250) 496-4135

27 November 2014 Province of British Columbia

Ministry of Forests, Lands and Natural Resource Operations

2nd floor, 441 Columbia Street

Kamloops BC, V2C 2T3

Attn: Dave McBeth, RPF

A/Director, Resource Management

Thompson-Okanagan Region

Re: Alwin Tailings Dam

Independent Third Party Review of Dam Safety Inspection

1. INTRODUCTION

This letter presents the observations and conclusions of a third party review of the dam safety

inspection (DSI) of the Alwin tailings dam. The review was carried out in accordance with Klohn Crippen

Berger (KCB) Subconsultant Agreement dated November 24, 2014. The third party review was

mandated by the British Columbia Ministry of Energy and Mines (MEM), Chief Inspector’s Orders, dated

August 18, 2014, which stipulated that a DSI be carried out to cover all dam structures for all tailings

storage facilities in British Columbia, and that the DSI must be reviewed by an independent qualified

engineer from a firm that has not been associated with the tailings dam. The Independent Third Party

Review must include a review of the dam consequence classification.

The DSI of the Alwin tailings dam was carried out by KCB, dated November 2014 (Klohn Crippen Berger,

2014). This third party review is based on that DSI. No site visit was made for the third party review.

2. BACKGROUND

Alwin Mine is located about 18 km west of Logan Lake, BC, and just west of the Highland Valley Copper

operations. The mine operated in 1972, milling about 77,000t and in 1981, milling about 155,000t (Kerr

2006). Tailings from these operations were disposed in the tailings storage facility (TSF), formed by

construction of the dam. No mining or milling have been done on the property since 1981.

The dam was constructed in 1971 under the direction of CBA Engineering. The initial tailings dam was

about 10 ft. high, with a crest elevation of 5060 ft. The dam was raised by downstream construction in

1980 to its current crest elevation of 5081 ft., with the raise design prepared by Herman Fellhauer,

P.Eng. The maximum height of the dam, from crest to downstream toe, is about 35 ft. The crest length

is about 1000 ft. (305m). In 1982 a spillway was constructed in the north abutment of the dam, with the

invert at elevation 5076 ft. The spillway was also designed by Herman Fellhauer.

The TSF is currently filled with water to about the level of the spillway. The tailings surface is reported

to be about 20 ft. below the water surface. The TSF pond is now referred to as Little OK Lake. The lake

Alwin Tailings Dam Independent Third Party Review of Dam Safety Inspection of TSF 27 November 2014

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is used as a recreational fishery. Island Lake, also known as Big OK Lake, is downstream of Little OK

Lake. Island Lake is known as a trophy fishery for large trout.

The Alwin tailings dam was previously assigned a consequence classification of “LOW” by MEM

personnel. KCB suggests that classification should be reviewed, since the facility has undergone a

change of use from a tailings facility to a recreational fishing lake.

3. 2014 DAM SAFETY INSPECTION

Neil Singh, P.Eng. and Emma Hill of KCB visited the site on October 29, 2014 to undertake the Dam

Safety Inspection. They provided a good photographic record of the dam.

Significant findings of the 2014 DSI included:

The embankment slopes and crest appeared in good condition, with no signs of significant

deformation or erosion

Minor seepage was noted downstream of the dam. The seepage reports to the seepage

recovery pond which was reported to be in satisfactory condition. Oil barrels and other debris

were noted in the area of the seepage pond.

The spillway was noted to have been partly infilled with road surfacing material that has raised

the spillway invert above its design level

An open adit was noted near the old mill, representing a public safety hazard.

Recommendations of the 2014 DSI were as follows:

Geotechnical inspector to discuss abandonment and responsibility for this impoundment with

colleagues at MEMPR and MELP. At this time, the bond on the defaulted permit should be

retained.

Clean up oil barrels and debris near the seepage pond

Remove excess road surfacing in spillway and confirm spillway invert is at 5076 ft. elevation, or

demonstrate that dam has sufficient freeboard and spillway has sufficient capacity

Prepare an OMS manual for the facility or demonstrate that it is not required

Locate as-built drawings or prepare new ones using an updated survey

Confirm if geotechnical review by C.O. Brawner exists and if so, locate it and review

Carry out a DSR to review the dam classification

Confirm if there are functional instruments and if so, locate them and obtain readings

Define monitoring and instrument readings frequency for Alwin Dam and include in OMS

Define monitoring frequency of flow rates and water quality measurements

Remove trees and bushes in spillway channel

Alwin Tailings Dam Independent Third Party Review of Dam Safety Inspection of TSF 27 November 2014

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REFERENCES

British Columbia Ministry of Energy and Mines, August 2013. Guidelines for Annual Dam Safety

Inspection Reports.

Canadian Dam Association, 2007. Dam Safety Guidelines.

Canadian Dam Association, 2014. Mining Dams Technical Bulletin.

Kerr, John R., P.Eng. 2006. Summary Report on the Alwin Property, Kamloops Mining Division, British

Columbia, report prepared for Max Investments Inc., on behalf of San Marco Resources Inc., November

15, 2006.

Klohn Crippen Berger, 2014. Alwin Tailings Dam, 2014 Dam Safety Inspection, report prepared for

Province of British Columbia Ministry of Energy and Mines, November 2014.